Conversion of asphaltene-containing charge stocks

ABSTRACT

ASPHALTENE - CONTAINING HYDROCARBONACEOUS CHARGE STOCKS ARE CONVERTED VIA A COMBINATION PROCESS WHICH INVOLVES (1) HYDROGENATIVE CONVERSION UTILIZING UNSUPPORTED, NON-STOICHIOMETRIC VANADIUM SULFIDE CATALYST, FOLLOWED BY (2) SOLIDS EXTRACTION OF THE PRODUCT EFFLUENT TO RECOVER THE VANADIUM SULFIDE CATALYST INTERSPERSED AMONG ASPHALTENES.

CONVERSION OF ASPHALTENE-CONTAINING CHARGE STOCKS Filed Oct. 18, 1971 BSG mmxumb United States Patent nice U.S. Cl. 208-95 9 Claims ABSTRACT F THE DISCLOSURE Asphaltene containing hydrocarbonaceous charge stocks are converted via a combination process which involves (1) hydrogenative conversion utilizing unsupported, non-stoichiometric vanadium sulfide catalyst, followed by (2) solids extraction of the product efuent to recover the vanadium sulfide catalyst interspersed among asphaltenes.

APPLICABILITY OF INVENTION The invention herein described is adaptable to a process for the conversion of asphaltene-containing hydrocarbonaceous charge stoclcs into lower-boiling hydrocarbon products. More specifically, the present invention is directed toward a combination process for continuously converting atmospheric tower bottoms products, vacuum tower bottoms products (vacuum residuum), crude oil residuum, topped crude oils, coal oil extracts, crude oils extracted from tar sands, etc., all of which are commonly referred to in the petroleum refining art as black oils.

These black oils contain high molecular weight sulfurous compounds in exceedingly large quantities and, in addition, excessive amounts of nitrogenous compounds, high molecular weight organometallic complexes principally comprising nickel and vanadium, and asphaltic material. Asphaltic material is generally found to be complexed, or linked with sulfur and, to a certain extent, with the organometallic compounds. An abundant supply of such hydrocarbonaceous material exists, most of which has a gravity less than about 20.0 API; a significant quantity has a gravity less than about 10.0 API. Black oils are generally characterized =by a boiling range indicating that 10.0% by volume, and generally more, has a normal boiling point above a temperature of about 1050 F.

The combination process of the present invention is particularly directed toward the conversion of black oils into distillable hydrocarbon products. Specific examples of the black oils, illustrative of those to which the present invention is especially applicable, include a vacuum tower bottoms product having a gravity of 7.1 API, containing 4.05% by weight of sulfur and 23.7% by weight of asphaltenes; and, a vacuum residuum having a gravity of 8.8" API, containing 3.0% by weight of sulfur, 4,300 p.p.m. of nitrogen and having a 20.0% volumetric distillation temperature of 1055 F. The use of the present invention affords the conversion of the majority of such material, heretofore having been believed virtually impossible, Which conversion is accompanied by a decrease in the rate of catalyst deactivation. The principal difficulty, heretofore experienced, resides in the lack of a technique which affords many catalytic composites a required degree of sulfur stability while simultaneously producing lowerboiling products from the asphaltic material.

l OBJECTS AND EMBODIMENTS One object of the present invention is to provide a more eicient process for the hydrogenative conversion of heavy hydrocarbonaceous material containing asphaltenes. A

37,723,297 Patented Mar. 27, 1973 corollary objective is to increase the effective life of the solid catalytic composite utilized in the process.

Another objective is toconvert hydrocarbon-insoluble asphaltenes into hydrocarbon-soluble, lower-boiling normally liquid products.

A specific object is to effect the continuous decontamination of asphaltenic black oils by providing a combination process utilizing a solid, unsupported catalyst, in which process there exists a significant decrease in the rate of catalyst deactivation.

In one embodiment, therefore, the present invention involves a process for the conversion of an asphaltenecontaining hydrocarbonaceous charge stock which comprises the steps of: (a) reacting said charge stock and hydrogen with non-stoichiometric vanadiumsulde in admixture with asphaltenes, at conversion conditions selected to convert insoluble asphaltenes into lower-boiling hydrocarbons; (b) deasphalting the resulting product effluent with a selective solvent in a solvent extraction zone to provide (l) a solvent-rich normally liquid phase and (2) a solvent-lean mixture of non-stoichiometric vanadium sulfide and asphaltenes; and, (c) recycling said mixture to combine with said charge stock.

yOther embodiments of our invention relate primarily to operating conditions and the selected solvents used within the solvent extraction zone. In one such embodiment, the charge stock is admixed with non-stoichiometric vanadium sulfide in an amount of at least 1.5 by Weight, calculated as elemental vanadium; the preferred upper limit, for the concentration of the non-stoichiometric vanadium sulfide is about 25.0% by weight.

PRIOR ART The basic concept involving the use of unsupported, non-stoichiometric vanadium sulde as the catalytic agent for the conversion of asphaltene-containing hydrocarbonaceous black oils, is found in our U. S. Pat. No. 3,558,474 (Class 2084108). As indicated in the teachings of this patent, the non-stoichiometrc vanadium sulfide exhibits an unusual degree of activity with respect to asphaltene conversion, while simultaneously eliminating a significant amount of the sulfurous and nitrogenous compounds. With respect to the present combination process, it should be noted that there exists no mention of solvent deasphalting, or extraction of the product effluent from the process.

Candor compels recognition of the fact that the prior art is replete With a wide variety of techniques for effecting solvent deasphalting of asphaltene-containing hydrocarbonaceous charge stocks. In the interest of brevity, no attempt will be made herein to exhaustively delineate the solvent deasphalting art.

U.S. Pat. No. 2,002,004 (Class 208-14) involves a twostage deasphalting process wherein the second stage completes the precipitation of asphalts which was only partially effected in the first stage. As above set forth, the solvents include naphtha, gasoline, casinghead gasoline and liquefied normally gaseous hydrocarbons, such as ethane, propane, butane and mixtures thereof.

U.S. Pat. No. 2,914,457 (Class 208-79) describes a multiple combination process involving fractionation, vacuum distillation, solvent deasphalting, hydrogenation and catalytic reforming. Again, the suitable liquid deasphalting solvents include liquefied normally gaseous hydrocarbons such as propane, n-butane, isobntane, or mixtures thereof, as well as ethane, ethylene, propane, propylene, n-butylene, isobutylene, pentane, isopentane, and mixtures thereof.

While the foregoing examples of the deasphalting art serve to indicate the now ancient use of the Wide variety of deasphalting solvents, it must be noted that there is no awareness of the present combination process wherein the charge stock is initially reacted with hydrogen in the presence of a catalytic composite, and certainly not with non-stoichiometric vanadium sulfide.

Mention should be made of U.S. Pat. No. 2,975,121 (Class 208-251) wherein the charge stock is initially subjected to hydrogenative cracking, followed by solvent deasphalting of the hydrogen-treated oil to remove suspended solid metal constituents. This reference indicates that the hydrogenation operation, for the initial treatment of the metal-containing charge oil may be carried out in the presence of a suitable hydrogenation catalyst, and preferably one which is a sulfide-resistant hydrogenation catalyst. Only two catalysts are disclosed, nickel tungsten sulfide and cobalt molybdate. There is, however, no recognition of the present combination process wherein the catalytic composite is non-stoichiometric vanadium sulfide, and the deasphalting operation produces an admixture of the vanadium sulfide with the precipitated asphaltenes.

SUMMARY OF INVENTION As indicated in U.S. Pat. No. 3,558,474, unsupported vanadium sulfide catalyst, colloidally dispersed in the hydrocarbonaceous charge stock, has been found to be an effective hydrorefining catalyst. The catalyst is non-stoichiometric, and is prepared in situ from the catalyst precursor, vanadium tetrasulfide. The indicated procedure is to disperse finely divided vanadium tetrasulfide in the charge, thermally decomposing the same in the presence of hydrogen to yield the non-stoichiometric vanadium sulfide catalyst. We have found, when the catalyst is separated from the product efiluent and rerun with additional charge stock, that a marked decrease in catalyst activity occurs.

Unsupported, non-stoichiometric vanadium sulfide catalyst has little, if any, internal surface area, and, therefore, the reactions must take place on the external surface. Consequently, the activity of the catalyst is principally dependent upon particle size. High catalytic activity is initially obtained when the catalyst is formed from the catalyst precursor, vanadium tetrasulfide. The finely dispersed vanadium tetrasulfide breaks down into even smaller particles when thermally decomposed in the presence of hydrogen. The present inventive concept is founded upon recognition of the fact that, when the catalyst precursor is thermally decomposed in the presence of hydrogen and asphaltenes, the resulting vanadium sulfide particles become associated with asphaltenes which serve to keep the catalyst colloidally dispersed. The high catalytic activity can be maintained provided that the catalyst particles are not permitted to agglomerate which is the case when the once-used catalyst is rerun to combine with additional charge stock.

In those instances where a high asphaltene conversion is obtained, resulting in insufficient asphaltenes in the product to associate with the catalyst particles, or if the catalyst is separated from the liquid product in a manner which removes the catalyst from any asphaltenes associated with it, the catalyst particle will subsequently agglomerate resulting in loss of external surface and consequently a decrease in catalytic activity. If, on the other hand, a too low asphaltene conversion is obtained, leading to coke deposition on the catalyst from the thermal decomposition of asphaltenes, or if the catalyst is separated from the liquid product in a manner such that carbonlzation of the catalyst is effected, a similar decrease in catalytic activity will result.

We have found that the activity of the non-stoichiometric vanadium sulfide catalyst, when it is re-used with fresh hydrocarbonaceous black oil, can be maintained close to the same level as when the catalyst is initially formed from the catalyst precursor, vanadium tetrasulfide. This is accomplished by initially processing the charge stock at conditions of operation which do not effect complete conversion of all the asphaltenic compounds. As the process continues in operation, 100.0% by weight of the virgin asphaltenes will be converted; however, this is not to be construed as stating that 100.0% by weight of all the asphaltenes entering the conversion zone are converted. When the conversion zone product efiiuent is subjected to solvent deasphalting, there is recovered a solvent-rich phase containing the normally liquid product essentially free of catalyst and asphaltics, and a solvent-lean heavy phase containing the vanadium sulfide catalyst in admixture with the unconverted asphaltenes. This solvent-lean heavy phase is then recycled to combine Iwith the hydrocarbonaceous charge stock and hydrogen, and introduced therewith into the conversion reaction zone. In this manner, the vanadium sulfide caatlyst is maintained in a nely dispersed state, being associated constantly with asphaltenes, and does not tend to form large agglomerates which lead to a decline in catalyst activity.

The concentration of non-stoichiometric vanadium sulfide, within the charge stock, is at least about 1.5% by weight thereof, calculated on the basis of elemental vanadium. Excessive concentrations do not appear to enhance the overall results, even with extremely contaminated charge stocks exhibiting an extremely high asphaltene content. Therefore, the upper limit of the vanadium sulfide is about 25.0% by weight. The colloidal slurry of catalyst and charge stock is admixed with hydrogen in an amount above about 5,000 s.c.f./bbl. of charge stock. The practical upper limit for hydrogen concentration is about 50,000 s.c.f./bbl. Following suitable heat-exchange with various hot eiuent streams, the temperature of the mixture is further increased to the level desired at the inlet to the reaction zone. Since the reactions being effected are principally exothermic, the temperature of the efliuent from the reaction zone will be the inlet temperature will be controlled in the range of about 325 C. to about 400 C. The residence time in the reaction zone is such that the outlet temperature is not higher than about 500 C. Although suitable results are obtained at a maximum reaction temperature of 500 C., a preferred mode of operation limits the maximum reaction temperature to about 450 C. The reaction zone will be maintained under an imposed pressure of about 500 p.s.i.g. to about 5,000 p.s.i.g.

Although the' present process may be effected in an elongated reaction zone with the slurry and hydrogen being introduced into the upper portion thereof, the eiuent being removed from a lower portion, an upfiow system is more advantageous. One principal advantage resides in the fact that the extremely heavy portion of the charge stock, particularly that portion having a normal boiling point above about 1050 F., has an appreciably longer residence within the reaction zone, with the result that a greater degree of conversion thereof is attainable.

The product efiiuent, including the vanadium sulfide catalyst and unreacted asphaltenes, is introduced into a suitable separation system from which a hydrogen-rich gaseous phase is recovered for purposes of recycle to combine with fresh feed charge stock. The hydrogen separation system is not considered an essential feature of the present combination process. It may consist of one or more suitably operated vessels from which the hydrogen is recovered; other normally gaseous streams may be separately recovered, including a methane/ethane concentrate and a butane/ propane concentrate. The normally liquid portion of the product efiiuent, again including the vanadium sullide catalyst and unreacted asphaltenes, is introduced into the upper portion of a solvent deasphalting zone, wherein it countercurrently contacts a suitable selective solvent which is introduced into the lower portion thereof. The solvent deasphalting zone will function at a temperature in the range of about 50 F. to about 500 F., and preferably from about F. to about 350 F.; the pressure will be maintained within the range of about 100 to about 1,000 p.s.i.g., and preferably from about 200 to about 600 p.s.i.g. The precise operating conditions will generally depend upon the physical characteristics of the normally liquid product eluent as well as the selected solvent. In general the temperature and pressure are selected to operate the deasphalting in liquid phase, and to insure that all the catalyst particles are removed in the solvent-lean heavy phase. Suitable solvents include those hereinbefore described with respect to the discussion of the prior art. Thus, it is contemplated that the solvent will be selected from the group of light hydrocarbons such as ethane, methane, propane, butane, isobutane, pentane, isopentane, neo-pentane, hexane, isohexane, heptane, etc. Similarly, the solvent may be a normally liquid naphtha fraction containing hydrocarbons having from about to about 14 carbon atoms per molecule, and preferably a naphtha fraction having an end boiling point below about 200 F. The solvent-rich normally liquid phase is introduced into a suitable solvent recovery system, the design and techniques of which are thoroughly described in the prior art.

Black oil conversion appears to be beneficially affected when carried out in the presence of hydrogen sulide. Therefore, it is within the scope of the present invention that from about 2.5 mol percent to about 25.0 mol percent hydrogen sulfide be present in the hydrogen being admixed with the charge stock/catalyst slurry.

DESCRIPTION OF DRAWING One embodiment is presented in the accompanying drawing by means of a simplified flow diagram in which details such as pumps, instrumentation and controls, heatexchange and heat-recovery circuits, valving, startup lines and similar hardware have been omitted as not essential to an understanding of the techniques involved. The utilization of such miscellaneous appurtenances, to modify the illustrated process flow, are well within the purview of those skilled in the art.

With reference now to the drawing, the charge stock in line 1 is admixed with recycle hydrogen from line 2 which is inclusive of make-up hydrogen being introduced via line 3. Non-stoichiometric vanadium sulfide catalyst, in admixture with asphaltenes, is introduced into line 1 by way of line 4, the entire mixture continuing through line 1 into the lower portion of reaction zone 5. The total product effluent, inclusive of the vanadium suliide catalyst and unreacted asphaltenes, is removed from reaction zone S by way of line 6, and introduced into a suitable hydrogen separation system 7. As hereinbefore set forth, hydrogen separation system 7 may be a multiple-vessel separation system wherein hydrogen is removed by way of line 2 for recycle to combine with the charge stock in line 1, and other gaseous components are removed from the process. In any event, the normally liquid product effluent, for example, hexane-plus hydrocarbonaceous material, including the vanadium sulfide catalyst and unreacted asphaltenes, is withdrawn from hydrogen separation zone 7 through line 8 and introduced thereby into the upper portion of deasphalting zone 9.

A suitable selective solvent, for example nebutane, is introduced into a lower portion of deasphalting zone 9 through line 10 and is inclusive of make-up solvent being introduced via line 11. The solvent-rich, normally liquid material is withdrawn from the upper portion of deasphalting zone 9 by way of line 12, and introduced into solvent recovery system 13 from which the recovered solvent is recycled by way of line 10. The normally liquid product effluent is withdrawn from the -process by way of line 14. The precipitated, vanadium sulfide catalyst and unreacted asphaltenes are withdrawn from deasphalting zone 9 and recycled through line 4 to combine with the charge stock and hydrogen. In view of the fact that most black oil charge stocks contain signiiicant quantities of metals, principally nickel and vanadium which exist as metallic porphyrins, a drag stream will be withdrawn through line 15, and sent to a suitable metals recovery unit. This technique prevents an undue build-up of metals within the system.

EXAMPLES The hydrocarbonaceous charge stock employed in these examples was a vacuum column bottoms having a gravity of 6.2 API, an initial boiling point of 546 F. and a 10.0% volumetric distillation temperature of 958 F.; 24.0% by volume was distillable at a temperature of 1050 F. The charge stock contained 13.3% by weight of asphaltenes, 4.88% by weight of sulfur, 0.48% by weight of nitrogen, 400 p.p.m. of vanadium and 70 p.p.m. of nickel, the latter existing as organometallic porphyrins.

Example I In this example, the charge stock was employed in an amount of 200 grams per hour, and was admixed with 18.9 s.c.f./hour of hydrogen (15,000 s.c.f./bbl.); the mol percent hydrogen sulfide in the recycle gas was 17.0. The reaction zone was maintained at a pressure of 3,000 p.s.i.g. and a peak reaction zone temperature of 443 C. The normally liquid portion of the product effluent was subjected to deasphalting, utilizing propane, `at a temperature of 67 C. and a pressure suicient to maintain the deasphalting operation in liquid phase.

The catalyst was initially employed in an amount of about 3.2% by weight for the conversion of a topped crude oil having a gravity of 8.9 API. The crude contained 10.53% by weight of asphaltenes, 2.80% by weight of sulfur and 578 p.p.m. of metals. The vanadium sulfide catalyst was rerun twice following removal of all benzene-soluble material .and asphaltenes. The results are given in the following Table I:

TABLE I.-TOPPED CRUDE PROCESSING Gravity, Sulfur; API Asphaltics wt. percent Run Number:

TABLE II.-VACUUM BOTTOMS PROCESSING, A

Gravity, Sulfur, API Asphaltics wt. percent Run Number:

The catalyst deactivation is particularly noticeable with respect to the residual asphaltic concentration; with fresh catalyst, more than 99.0% of the virgin asphaltenes were converted, while the above ligures indicate about 87.0% asphaltene conversion.

'Example II For the next series of runs, the catalyst concentration was decreased to a level of 2.8% to 3.5% by Weight, again calculated as elemental vanadium, and the temperature decreased to a level within the range of about 425 C. to about 430 C. The only other operational change was in accordance with the -process of the present invention wherein the catalytic vanadium suliide was immediately recycled from the deasphalter with the unreacted asphaltenes.

The vanadium suliide catalyst was rerun twice; the catalyst concentration in the initial run (7) was 3.5% by Weight, and in the two reruns (8 and 9), 2.8% by weight. The results are presented in the following Table III:

TABLE IIL-VACUUM BOTTOMS PROCESSING, B

Gravity, Sulfur, API Asphaltics wt. percent These results clearly indicate the benefits afforded through the utilization of the present combination process, and are totally unexpected in view of the fact that the catalyst concentration had been decreased from a level of 7.9% to about 2.8% by weight.

We claim as our invention:

l. A process for the conversion of an asphaltene-containing hydrocarbonaceous charge stock which comprises the steps of (a) reacting7 said charge stock and hydrogen with nonstoichiometric vanadium sulfide in admiXture with asphaltenes, at conversion conditions selected to convert insoluble asphaltenes into lower-boiling hydrocarbons;

(b) deasphalting the resulting product eticluent with a selective solvent in a solvent extraction zone to provide (l) a solvent-rich normally liquid phase and (2) a solvent-lean mixture of non-stoichiometric vanadium sulfide and asphaltenes; and,

(c) recycling said mixture to combine with said charge stock.

2. The process of claim 1 further characterized in that said conversion conditions include a temperature from about 300 C. to about 500 C. and a pressure in the range of about 500 p.s.i.g. to about 5,000 p.s.i.g.

3. The process of claim 1 further characterized in that said charge stock is admixed with non-stoichiometric vanadium sulfide in an amount of at least 1.5% by weight, calculated as elemental vanadium.

4. The process of claim 1 further characterized in that the hydrogen concentration, with respect to said charge stock, is at least about 5,000 s.c.f./ bbl.

5. The process of claim 1 further characterized in that said selective solvent is a light hydrocarbon containing from one to about seven carbon atoms per molecule.

6. The process of claim 1 further characterized in that said selective solvent is a normally liquid naphtha fraction containing hydrocarbons having from about tive to about fourteen carbon atoms per molecule.

7. The process of claim 1 further characterized in that the volume ratio of said selective solvent to said charge stock is from about 3:1 to about 15:1.

8. The process of claim 5 further characterized in that said selective solvent is n-butane.

9. The process of claim 6 further characterized in that said na-phtha fraction has an end boiling point below about 200 F.

References Cited UNITED STATES PATENTS HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 208-108, 309 

